LOW-TEMPERATURE ASHING OF BULGARIAN LIGNITES

The characterisation of mineral components of coals requires their iso lation from organic matter, which would otherwise interfere with phase identification by means of physico-chemical techniques. Low-temperatu re ashing (LTA) using a cool oxygen plasma is a prospective method to oxidise coal organic matter at low temperatures while keeping the mine ral constituents unaltered. In this work we have used a microwave-exci ted plasma apparatus for the LTA treatment of lignite samples from the Maritza-Iztok (M-I-1; M-I-2) and Elhovo basins. Minerals were charact erised in the LTA residues using FT-IR spectroscopy, X-ray diffraction and scanning electron microscopy combined with energy-dispersive X-ra y microanalysis. The advantages and disadvantages of the LTA method ar e discussed. Results indicate that LTA performs well for the isolation of mineral matter, the ensuing methodology being adequate for the cha racterisation of Bulgarian lignites. The same mineral constituents (pr incipally clay minerals, quartz, pyrite and carbonates) were identifie d in all the three studied samples, differences being mainly in their particle size, degree of crystallinity and distribution in the organic matter of coals.